802.1BR defines that a switch with port expanding capability may consist of a Controlling Bridge (CB) and a plurality of Port Extenders (PEs) which connected with each other in a tree manner. The PEs are configured to expand port quantity and port accessing capability for the CB. For example, a PE may be connected with a CB or an upper PE through an upstream port, and connected with a lower PE through a cascade port. Two PEs may be cascaded with each other. For example, a CB may be connected with a plurality of PEs through cascade ports and configured to manage Virtual Port (vPort) mapping for ports on the PEs. For forwarding a packet, the PE may load an Ethernet-Tag (E-TAG) carrying an E-Tag Channel Identifier (ECID) associated to a source port through which the packet is received into the packet and then send the packet to the CB, so that the CB may decide how to forward the packet.